The Diamondbacks have finalized their roster for the NLDS against the Brewers and according to Jack McGruder of FOX Sports Arizona, rookie right-hander Jarrod Parkerhas made the final cut.

Parker, who was just promoted from the minors in September, gave up four hits over 5 2/3 shutout innings Tuesday in his major league debut against the Dodgers. The 22-year-old isn’t getting the Matt Moore treatment, though, as Diamondbacks manager Kirk Gibson intends to use him out of the bullpen for now.

After missing the entire 2010 season following Tommy John surgery, Parker posted a 3.79 ERA and 112/55 K/BB ratio over 130 2/3 innings with Double-A Mobile this season. The 2007 first-round pick has top-of-the-rotation potential in the long-term.

I was under the very distinct impression that the cut off date for adding people to the roster was sometime in August or early September, after which no additions for the playoffs may be made. Is this correct or am I not understanding? I’m not complaining about Parker, just confused.

Basically, players who are on the 60-man are eligible for the postseason, but they can also be replaced by someone who is in the organization on August 31 and on the 40-man roster. Parker fits both criteria, so they can essentially swap him out for Marquis, Drew, Juan Gutierrez, etc. Very common.